A solution is 0.10 M in CH3COOH (K_a = 1.8x10^-5) and 0.10 M in HCOOH (K_a = 1.8x10^-4). Using [H+] = sqrtK_1C_1+K_2C_2, find the pH (two decimals).

JEE Main levelNumerical answerDifficulty 2 of 3ia191

A solution is $0.10 M$ in $CH X_{3} COOH$ ( $K_{a} = 1.8 \times 1 0^{- 5}$ ) and $0.10 M$ in $HCOOH$ ( $K_{a} = 1.8 \times 1 0^{- 4}$ ). Using $[H X^{+}] = K_{1} C_{1} + K_{2} C_{2}$ , find the pH (two decimals).

Numerical answer type, tolerance 0.01.

[H X^{+}] = 1.8 \times 1 0^{- 5} \times 0.10 + 1.8 \times 1 0^{- 4} \times 0.10 = 1.98 \times 1 0^{- 5} = 4.45 \times 1 0^{- 3} M

. So

pH = 2.35